Various ways of folding sheets, and more particularly of sheets being continuously supplied from the printing machines, are known. In one such apparatus, the leading edge of a sheet is gripped by grippers positioned on the circumference of a sheet pick-up drum. The sheet pick-up drum is provided with a mechanism which includes a creasing blade which can protrude from the circumference of the pick-up drum when controlled to do so at a predetermined angular position. The pick-up drum is in running contact with the circumference of a sheet receiving cylinder which has a groove. The sheet receiving cylinder and the pick-up drum are driven in synchronism. The leading edge of the sheet, after having been gripped, is passed through the nip between the pick-up cylinder and the receiving cylinder. At the point of creasing, the creasing blade is caused to protrude from the pick-up cylinder at the instant of time when a creasing groove on the sheet receiving cylinder passes the nip, thus pushing a creased portion of the sheet into the groove of the sheet receiving cylinder which, upon release of the leading edge of the sheet from the pick-up cylinder, will then transport the folding sheet for further handling and conveying.
Apparatus of this type should be so designed that the leading edge gripper mechanism and the creasing blade mechanism can be relatively rotated along the circumferential position of the pick-up cylinder in order to accomodate sheets of different length, and still cause the crease to occur at the midpoint of the sheet, or at another predetermined longitudinal position thereof. It is thus desirable to be able to adjust the relative position of the sheet grippers and the creasing blade with respect to their relative circumferential position on the pick-up cylinder.
One type of known structure utilizes a split intermediate wheel or gear which, after loosening a screw connection, permits relative adjustment of the gears with respect to each other, permitting in turn rotation of the cutting cylinder which rotates a cutter blade to cut the web into sheets, and relative angular adjustment, further, of the creasing blade with respect to the grippers. It has been proposed to utilize an intermediate gear with helical gear teeth in order to permit fine adjustment, and so position the intermediate gear that its axial location on its shaft can be shifted, so that the spiral or helical gears will provide fine adjustment of angular positions. The adjustment obtained in this manner is smoothly continuous, that is, not in steps. Adjustment is done by hand. A considerable amount of skill as well as operating strength is required of the printing machine operator in order to effect proper adjustment.
Another way of providing rotary creasing and folding of a sheet and subsequent transport, while permitting relative adjustment, is shown in German Patent No. 739,360, in which the disadvantages of high skill and force requirements are intended to be avoided by use of a planetary gear drive. The planetary gear drive also permits smooth continuous adjustment of a creasing blade with respect to the grippers of the pick-up cylinder. This adjustment arrangement has the disadvantage that fine adjustment is difficult if the adjustment path or distance itself is small. Planetary gear drives, after only comparatively short operating time, tend to develop gear play, which results in inaccuracies in folding and creasing of the sheet. Additionally, planetary gear drives are noisy and wasteful of energy.
German Patent Disclosure Document DE-OS No. 21,57,615 illustrates an arrangement in which the adjustment between grippers and the creasing blade is so made that a dual intermediate wheel is provided in which the gear teeth have the same transmission ratio with respect to associated gears, and each gear wheel is connected with a rotating gear portion of a separate transmission gearing. The rotating gears of the transmission gearings are coupled together. The stator of one of the transmission gearings is fixed, the other stator, however, being adjustable angularly by a positioning motor or by hand. In accordance with this teaching, the gear transmissions-- which are known as such--should have transmission ratios of, for example 160:161.
The folding device disclosed in this German Disclosure Document does not avoid the disadvantages mentioned above. They are reduced in part, but other difficulties arise. A planetary gear is still necessary which, in order to maintain the desired adjustment in operation, must rotate continuously. Planetary gears require additional bearings and gear engagement points, so that, as a final result, overall there is little improvement in the efficiency of operation or noise level. The aim in all printing--exact registration and reproducible operation--cannot be achieved upon extended operating time due to play and wear and tear in the gearing, and at the gear engagement points. The additional gear engagement locations, due to the multiple gears used in planetary drives, and the consequent small and hence rapidly rotating gears, cause an increase in operating noise. The folding device, in order to be adjustable, additionally requires substantial space. For complete adjustment of the format, it is necessary to utilize two of the devices as explained in the aforementioned German Disclosure Document, one for the gripper adjustment to adjust the gripper on the pick-up cylinder, and one for the creasing blade in order to position the creasing blade centrally of the sheet.